#include<stdio.h>
#include<string.h>
#include<stdlib.h>
char* mycat(char *cat1,char *cat2){
   char* s3=(char*)malloc(strlen(cat1)+strlen(cat2)+1);
   char* temp =s3;
   while(*cat1!='\0'){
   *s3++=*cat1++;
   }
   while(*s3++=*cat2++);
   return temp;
   free(s3);
    }
int main(int argc,char const* argv[]){
     char* s1="abcd";
     char* s2="efg"; 
     printf("%s",mycat(s2,s1));
     return 0;
}